WO2022264659A1 - Solid electrolyte material and battery - Google Patents

Abstract

A solid electrolyte material according to the present disclosure comprises a crystal phase that contains Li, Mg and X which is at least one element selected from the group consisting of F, Cl, Br and I; and the crystal phase has a crystal structure belonging to the space group Fm-3m. A battery 1000 according to the present disclosure comprises a positive electrode 201, a negative electrode 203, and an electrolyte layer 202 that is arranged between the positive electrode 201 and the negative electrode 203. At least one component selected from the group consisting of the positive electrode 201, the negative electrode 203, and the electrolyte layer 202 contains the solid electrolyte material according to the present disclosure.

Description

solid electrolyte materials and batteries

The present disclosure relates to solid electrolyte materials and batteries.

Patent Document 1 discloses LiAlI ₄ as a raw material for a lithium oxide halide solid phase electrolyte.

JP-A-57-103270

An object of the present disclosure is to provide a solid electrolyte material suitable for improving lithium ion conductivity.

The solid electrolyte material of the present disclosure is
containing a crystalline phase containing Li, Mg, and X;
here,
X is at least one selected from the group consisting of F, Cl, Br, and I;
The crystal phase has a crystal structure belonging to the space group Fm-3m.

The present disclosure provides a solid electrolyte material suitable for improving lithium ion conductivity.

FIG. 1 shows a cross-sectional view of a battery 1000 according to a second embodiment. FIG. 2 shows a schematic diagram of a pressure forming die 300 used to evaluate the ionic conductivity of solid electrolyte materials. 3 is a graph showing a Cole-Cole plot obtained by impedance measurement of the solid electrolyte material according to Example 1. FIG. FIG. 4 is a graph showing X-ray diffraction patterns of solid electrolyte materials according to Examples 1-3 and Comparative Examples 1-2. 5 is a graph showing the initial discharge characteristics of the battery according to Example 1. FIG.

Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

(First embodiment)
The solid electrolyte material according to the first embodiment contains a crystal phase containing Li, Mg, and X. X is at least one selected from the group consisting of F, Cl, Br and I; The crystal phase has a crystal structure belonging to the space group Fm-3m.

The solid electrolyte material according to the first embodiment is a solid electrolyte material suitable for improving lithium ion conductivity. The solid electrolyte material according to the first embodiment can for example have a practical lithium ion conductivity, for example a high lithium ion conductivity.

Here, the high lithium ion conductivity is, for example, 2.5×10 ⁻⁵ S/cm or more near room temperature. The solid electrolyte material according to the first embodiment can have an ionic conductivity of, for example, 2.5×10 ⁻⁵ S/cm or more.

The solid electrolyte material according to the first embodiment can be used to obtain batteries with excellent charge/discharge characteristics. An example of a battery is an all solid state battery. The all-solid battery may be a primary battery or a secondary battery.

The crystal phase may consist of Li, Mg, and X.

The crystal phase may contain elements that are unavoidably mixed. Examples of such elements are hydrogen, nitrogen or oxygen. Such elements can be present in the raw powder of the solid electrolyte material or in the atmosphere for manufacturing or storing the solid electrolyte material. Elements that are unavoidably mixed in the solid electrolyte material according to the first embodiment are, for example, 1 mol % or less.

The solid electrolyte material according to the first embodiment may consist essentially of Li, Mg, and X in order to increase the ionic conductivity of the solid electrolyte material. Here, "the solid electrolyte material according to the first embodiment consists essentially of Li, Mg, and X" means that the total amount of all elements constituting the solid electrolyte material according to the first embodiment It means that the total ratio of Li, Mg, and X substance amounts (that is, the molar fraction) is 95% or more.

In order to increase the ionic conductivity of the solid electrolyte material, the solid electrolyte material according to the first embodiment may consist of Li, Mg, and X only.

The crystal phase may have a sodium chloride type structure.

The crystal phase may further contain M in order to increase the ionic conductivity of the solid electrolyte material. Here, M is at least one selected from the group consisting of Al, Ga and In.

The solid electrolyte material according to the first embodiment may consist essentially of Li, Mg, M, and X in order to increase the ionic conductivity of the solid electrolyte material. Here, "the solid electrolyte material according to the first embodiment consists essentially of Li, Mg, M, and X" means the total amount of substances of all elements constituting the solid electrolyte material according to the first embodiment. to the total amount of Li, Mg, M, and X (ie, mole fraction) is 95% or more.

The solid electrolyte material according to the first embodiment may consist only of Li, Mg, M, and X in order to increase the ionic conductivity of the solid electrolyte material.

M may contain Al in order to increase the ionic conductivity of the solid electrolyte material. M may be Al.

　X may contain I in order to increase the ionic conductivity of the solid electrolyte material.

A large proportion of I in X can soften the solid electrolyte material. As a result, the contact area of the solid electrolyte material with other materials (for example, the active material) is increased, and the charge/discharge characteristics are improved. For example, the ratio of the amount of substance of I to the total amount of substance of X including I (i.e., mole fraction) may be 50% or more, may be 70% or more, or may be 90% or more. There may be. X may be I.

The solid electrolyte material according to the first embodiment may be a material represented by the following compositional formula (1).
Li2 _{-aMg1- aMaX4 ( 1} )
Here, 0≦a<1 is satisfied.

The material represented by compositional formula (1) has high ionic conductivity.

In order to increase the ionic conductivity of the solid electrolyte material, the composition formula (1) may satisfy 0≦a≦0.75, or may satisfy 0.50≦a≦0.75. good.

The upper and lower limits of a in composition formula (1) can be defined by any combination selected from numerical values of 0, 0.50, and 0.75.

In order to increase the ionic conductivity of the solid electrolyte material, X may contain I in the composition formula (1). X may be I.

The structure of the crystal phase can be confirmed, for example, by X-ray diffraction measurement of the solid electrolyte material.

The solid electrolyte material according to the first embodiment may further contain a crystal phase having a structure different from the crystal structure belonging to space group Fm-3m. For example, the solid electrolyte material according to the first embodiment may further contain a crystal phase having a _LiAlCl4 type structure. Incidentally, the LiAlCl ₄ -type structure belongs to the space group P2 ₁ /c.

The solid electrolyte material according to the first embodiment may be a mixture of crystalline and amorphous.

The shape of the solid electrolyte material according to the first embodiment is not limited. Examples of such shapes are acicular, spherical, or ellipsoidal. The solid electrolyte material according to the first embodiment may be particles. The solid electrolyte material according to the first embodiment may have the shape of pellets or plates.

When the shape of the solid electrolyte material according to the first embodiment is particulate (for example, spherical), the solid electrolyte material according to the first embodiment may have a median diameter of 0.1 μm or more and 100 μm or less. , a median diameter of 0.5 μm or more and 10 μm or less. Thereby, the solid electrolyte material according to the first embodiment and other materials can be well dispersed. The median diameter of particles means the particle diameter (d50) at which the cumulative volume is 50% in the volume-based particle size distribution. The volume-based particle size distribution is measured by, for example, a laser diffraction measurement device or an image analysis device.

<Method for producing solid electrolyte material>
The solid electrolyte material according to the first embodiment is produced, for example, by the following method.

For example, two or more iodide raw powders are mixed so as to have the desired composition.

As an example, when the target composition is _{Li1.25Mg0.25Al0.75I4} , the LiI raw powder, _MgI2 raw powder _, and _AlI3 raw powder _are generally LiI: _MgI2 : _{AlI3 =} 1.25: They are mixed in a molar ratio of 0.25:0.75. The raw powders may be mixed in pre-adjusted molar ratios to compensate for possible compositional variations in the synthesis process.

For example, increasing AlI ₃ increases the value of a in the composition formula (1).

Li metal, Mg metal, Al metal, and I ₂ may be used as raw materials.

A mixture of raw material powders is mechanochemically reacted with each other in a mixing device such as a planetary ball mill to obtain a reactant. That is, the raw material powders are reacted with each other using the method of mechanochemical milling. The reactants may be fired in vacuum or in an inert atmosphere. Alternatively, a mixture of raw material powders may be fired in vacuum or in an inert atmosphere to obtain a reactant.

By these methods, the solid electrolyte material according to the first embodiment is obtained.

The composition of the solid electrolyte material can be determined, for example, by atomic absorption spectrometry or high frequency inductively coupled plasma emission spectrometry. For example, the composition of Li can be determined by atomic absorption spectroscopy, and the composition of Mg, M and X can be determined by high frequency inductively coupled plasma atomic emission spectroscopy.

(Second embodiment)
A second embodiment will be described below. Matters described in the first embodiment may be omitted as appropriate.

A battery according to the second embodiment includes a positive electrode, an electrolyte layer, and a negative electrode. An electrolyte layer is disposed between the positive and negative electrodes. At least one selected from the group consisting of the positive electrode, the electrolyte layer, and the negative electrode contains the solid electrolyte material according to the first embodiment.

Since the battery according to the second embodiment contains the solid electrolyte material according to the first embodiment, it has excellent charge/discharge characteristics.

FIG. 1 shows a cross-sectional view of a battery 1000 according to the second embodiment.

A battery 1000 includes a positive electrode 201 , an electrolyte layer 202 and a negative electrode 203 . Electrolyte layer 202 is provided between positive electrode 201 and negative electrode 203 .

The positive electrode 201 contains positive electrode active material particles 204 and solid electrolyte particles 100 .

The negative electrode 203 contains negative electrode active material particles 205 and solid electrolyte particles 100 .

The solid electrolyte particles 100 are particles containing the solid electrolyte material according to the first embodiment. The solid electrolyte particles 100 may be particles containing the solid electrolyte material according to the first embodiment as a main component. A particle containing the solid electrolyte material according to the first embodiment as a main component means a particle in which the component contained in the largest molar ratio is the solid electrolyte material according to the first embodiment. The solid electrolyte particles 100 may be particles made of the solid electrolyte material according to the first embodiment.

The positive electrode 201 contains a material capable of intercalating and deintercalating metal ions such as lithium ions. The positive electrode 201 contains, for example, a positive electrode active material (eg, positive electrode active material particles 204).

Examples of positive electrode active materials are lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxyfluorides, transition metal oxysulfides, or transition metal oxynitrides. be. Examples of lithium-containing transition metal oxides are Li(Ni,Co,Mn) _O2 , Li(Ni,Co,Al) _O2 or _LiCoO2 .

In the present disclosure, "(A, B, C)" means "at least one selected from the group consisting of A, B, and C."

The positive electrode active material particles 204 may have a median diameter of 0.1 μm or more and 100 μm or less. When positive electrode active material particles 204 have a median diameter of 0.1 μm or more, positive electrode active material particles 204 and solid electrolyte particles 100 can be well dispersed in positive electrode 201 . Thereby, the charge/discharge characteristics of the battery 1000 are improved. When the positive electrode active material particles 204 have a median diameter of 100 μm or less, the diffusion rate of lithium in the positive electrode active material particles 204 is improved. This allows battery 1000 to operate at high output.

The positive electrode active material particles 204 may have a larger median diameter than the solid electrolyte particles 100 . Thereby, the positive electrode active material particles 204 and the solid electrolyte particles 100 can be well dispersed.

In order to increase the energy density and output of battery 1000, in positive electrode 201, the ratio of the volume of positive electrode active material particles 204 to the sum of the volume of positive electrode active material particles 204 and the volume of solid electrolyte particles 100 is 0.30 or more and 0 0.95 or less.

In order to increase the energy density and output of the battery 1000, the positive electrode 201 may have a thickness of 10 µm or more and 500 µm.

The electrolyte layer 202 contains an electrolyte material. The electrolyte material is, for example, a solid electrolyte material. The electrolyte layer 202 may be a solid electrolyte layer. The electrolyte layer 202 may contain the solid electrolyte material according to the first embodiment.

The electrolyte layer 202 may contain 50% by mass or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may contain 70% by mass or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may contain 90% by mass or more of the solid electrolyte material according to the first embodiment. The electrolyte layer 202 may consist only of the solid electrolyte material according to the first embodiment.

Hereinafter, the solid electrolyte material according to the first embodiment will be referred to as the first solid electrolyte material. A solid electrolyte material different from the first solid electrolyte material is referred to as a second solid electrolyte material.

The electrolyte layer 202 may contain not only the first solid electrolyte material but also the second solid electrolyte material. In the electrolyte layer 202, the first solid electrolyte material and the second solid electrolyte material may be uniformly dispersed. A layer made of the first solid electrolyte material and a layer made of the second solid electrolyte material may be stacked along the stacking direction of battery 1000 .

The electrolyte layer 202 may consist only of the second solid electrolyte material.

The electrolyte layer 202 may have a thickness of 1 μm or more and 1000 μm or less. When the electrolyte layer 202 has a thickness of 1 μm or more, the short circuit between the positive electrode 201 and the negative electrode 203 is less likely to occur. If the electrolyte layer 202 has a thickness of 1000 μm or less, the battery 1000 can operate at high power.

The negative electrode 203 contains a material capable of intercalating and deintercalating metal ions such as lithium ions. The material is, for example, a negative electrode active material (eg, negative electrode active material particles 205).

Examples of negative electrode active materials are metal materials, carbon materials, oxides, nitrides, tin compounds, or silicon compounds. The metallic material may be a single metal or an alloy. Examples of metallic materials are lithium metal or lithium alloys. Examples of carbon materials are natural graphite, coke, ungraphitized carbon, carbon fibers, spherical carbon, artificial graphite, or amorphous carbon. From the viewpoint of capacity density, suitable examples of negative electrode active materials are silicon (ie, Si), tin (ie, Sn), silicon compounds, or tin compounds.

The negative electrode active material particles 205 may have a median diameter of 0.1 μm or more and 100 μm or less. When negative electrode active material particles 205 have a median diameter of 0.1 μm or more, negative electrode active material particles 205 and solid electrolyte particles 100 can be well dispersed in negative electrode 203 . Thereby, the charge/discharge characteristics of the battery 1000 are improved. When the negative electrode active material particles 205 have a median diameter of 100 μm or less, the diffusion rate of lithium in the negative electrode active material particles 205 is improved. This allows battery 1000 to operate at high output.

The negative electrode active material particles 205 may have a larger median diameter than the solid electrolyte particles 100 . Thereby, the negative electrode active material particles 205 and the solid electrolyte particles 100 can be well dispersed.

In order to increase the energy density and output of the battery 1000, in the negative electrode 203, the ratio of the volume of the negative electrode active material particles 205 to the total volume of the negative electrode active material particles 205 and the volume of the solid electrolyte particles 100 is 0.30 or more and 0 0.95 or less.

In order to increase the energy density and output of the battery 1000, the negative electrode 203 may have a thickness of 10 µm or more and 500 µm or less.

At least one selected from the group consisting of positive electrode 201, electrolyte layer 202, and negative electrode 203 contains a second solid electrolyte material for the purpose of enhancing ion conductivity, chemical stability, and electrochemical stability. may be

The second solid electrolyte material may be a halide solid electrolyte.

Examples of halide solid electrolytes are Li ₂ MgX' ₄ , Li ₂ FeX' ₄ , LiAlX' ₄ , Li(Ga,In)X' ₄ or Li ₃ (Al,Ga,In)X' ₆ . Here, X' is at least one selected from the group consisting of F, Cl, Br and I.

Another example of a halide solid electrolyte _is the compound _represented by _{LipMeqYrZ6 .} Here p+m′q+3r=6 and r>0 are satisfied. Me is at least one selected from the group consisting of metal elements other than Li and Y and metalloid elements. Z is at least one selected from the group consisting of F, Cl, Br and I; The value of m' represents the valence of Me. "Semimetallic elements" are B, Si, Ge, As, Sb, and Te. "Metallic elements" are all elements contained in Groups 1 to 12 of the periodic table (excluding hydrogen), and all elements contained in Groups 13 to 16 of the periodic table (however, B, Si , Ge, As, Sb, Te, C, N, P, O, S, and Se). From the viewpoint of the ionic conductivity of the halide solid electrolyte, Me is selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. may be at least one.

The second solid electrolyte material may be a sulfide solid electrolyte.

Examples of sulfide solid electrolytes are Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , Li ₂ S-B ₂ S ₃ , Li ₂ S-GeS ₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , or _{Li10GeP2S12 . _}

The second solid electrolyte material may be an oxide solid electrolyte.

Examples of oxide solid electrolytes are
(i) NASICON _- type solid electrolytes such as _{LiTi2(PO4)3 or} elemental substitutions thereof;
(ii) perovskite-type solid electrolytes such as (LaLi) _TiO3 ;
₍ iii) _{LISICON -} type solid electrolytes such as _Li14ZnGe4O16 , _Li4SiO4 , _LiGeO4 or elemental substitutions thereof;
( _iv ) _{garnet -} type solid electrolytes such as _Li7La3Zr2O12 or its elemental substitutions, or ₍ v) _Li3PO4 or its N substitutions,
is.

The second solid electrolyte material may be an organic polymer solid electrolyte.

Examples of organic polymer solid electrolytes are polymeric compounds and lithium salt compounds. The polymer compound may have an ethylene oxide structure. Since a polymer compound having an ethylene oxide structure can contain a large amount of lithium salt, the ionic conductivity can be further increased.

Examples of lithium salts are _LiPF6 , _{LiBF4 , LiSbF6} , _LiAsF6 , _{LiSO3CF3, LiN(SO2CF3)2 , LiN ( SO2C2F5 ) 2 ,} LiN _{( SO2CF3} ). ( _SO2C4F9 ) _, or _{LiC ( SO2CF3} ) ₃ . One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used.

At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 is a non-aqueous electrolyte, a gel electrolyte, or an ion electrolyte for the purpose of facilitating the transfer of lithium ions and improving the output characteristics of the battery. It may contain liquids.

The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

Examples of non-aqueous solvents are cyclic carbonate solvents, chain carbonate solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, or fluorine solvents. Examples of cyclic carbonate solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of linear carbonate solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorosolvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Alternatively, a mixture of two or more non-aqueous solvents selected from these may be used.

Examples of lithium salts are _LiPF6 , _{LiBF4 , LiSbF6} , _LiAsF6 , _{LiSO3CF3, LiN(SO2CF3)2 , LiN ( SO2C2F5 ) 2 ,} LiN _{( SO2CF3} ). ( _SO2C4F9 ) _, or _{LiC ( SO2CF3} ) ₃ . One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used. The lithium salt concentration is, for example, 0.5 mol/liter or more and 2 mol/liter or less.

A polymer material impregnated with a non-aqueous electrolyte can be used as the gel electrolyte. Examples of polymeric materials are polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polymers with ethylene oxide linkages.

Examples of cations contained in ionic liquids are
(i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium;
(ii) aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums; or (iii) nitrogen-containing heteroatoms such as pyridiniums or imidazoliums ring aromatic cations,
is.

Examples of anions contained in the ionic liquid are PF ₆ ⁻ , BF ₄ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ , SO ₃ CF ₃ ⁻ , N(SO ₂ CF ₃ ) ₂ ⁻ , N(SO ₂ C ₂ F ₅ ) _2- ^, N( _SO2CF3 ) _{( SO2C4F9} ) ^- _, or _{C ( SO2CF3} ⁾ _3- .

The ionic liquid may contain a lithium salt.

At least one selected from the group consisting of the positive electrode 201, the electrolyte layer 202, and the negative electrode 203 may contain a binder for the purpose of improving adhesion between particles.

Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, Polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyether sulfone, hexafluoropolypropylene, styrene-butadiene rubber , or carboxymethyl cellulose. Copolymers can also be used as binders. Examples of such binders are tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ethers, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid , and hexadiene. A mixture of two or more selected from the above materials may be used as the binder.

At least one selected from the positive electrode 201 and the negative electrode 203 may contain a conductive aid for the purpose of increasing electronic conductivity.

Examples of conductive aids are
(i) graphites such as natural or artificial graphite;
(ii) carbon blacks such as acetylene black or ketjen black;
(iii) conductive fibers such as carbon or metal fibers;
(iv) carbon fluoride,
(v) metal powders such as aluminum;
(vi) conductive whiskers such as zinc oxide or potassium titanate;
(vii) a conductive metal oxide such as titanium oxide, or (viii) a conductive polymeric compound such as polyaniline, polypyrrole, or polythiophene;
is. For cost reduction, the conductive aid (i) or (ii) may be used.

Examples of the shape of the battery according to the second embodiment are coin-shaped, cylindrical, rectangular, sheet-shaped, button-shaped, flat-shaped, and laminated.

For the battery according to the second embodiment, for example, a material for forming a positive electrode, a material for forming an electrolyte layer, and a material for forming a negative electrode are prepared, and the positive electrode, the electrolyte layer, and the negative electrode are arranged in this order by a known method. It may also be manufactured by making laminated laminates.

The present disclosure will be described in more detail below with reference to examples.

(Example 1)
(Preparation of solid electrolyte material)
In an argon atmosphere having a dew point of -60°C or less (hereinafter referred to as "dry argon atmosphere"), LiI, MgI ₂ , and AlI ₃ as raw material powders were mixed with LiI:MgI ₂ :AlI ₃ =1.25:0. A molar ratio of 25:0.75 was provided. These raw powders were ground and mixed in a mortar. Thus, a mixed powder was obtained. The mixed powder was milled at 500 rpm for 12 hours using a planetary ball mill. Thus, the solid electrolyte material powder according to Example 1 was obtained.

The Li content per unit weight of the solid electrolyte material according to Example 1 was measured by atomic absorption spectrometry. The Mg content, Al content and I content of the solid electrolyte material according to Example 1 were measured by high frequency inductively coupled plasma atomic emission spectrometry. Based on the contents of Li, Mg, Al, and I obtained from these measurement results, the Li:Mg:Al:I molar ratio was calculated. As a result, the solid electrolyte material according to Example 1 had a Li:Mg:Al:I molar ratio of 1.25:0.25:0.75:4, similar to the molar ratio of the raw material powder. That is, the solid electrolyte material according to Example _{1 had} a composition represented _{by Li1.25Mg0.25Al0.75I4 .}

(Evaluation of ionic conductivity)
FIG. 2 shows a schematic diagram of a pressure forming die 300 used to evaluate the ionic conductivity of solid electrolyte materials.

The pressure forming die 300 had a punch upper part 301 , a frame mold 302 and a punch lower part 303 . Both the punch upper portion 301 and the punch lower portion 303 were made of electronically conductive stainless steel. The frame mold 302 was made of insulating polycarbonate.

Using the pressure molding die 300 shown in FIG. 2, the ionic conductivity of the solid electrolyte material according to Example 1 was measured by the following method.

In a dry atmosphere having a dew point of −30° C. or less, the solid electrolyte material powder according to Example 1 (that is, the solid electrolyte material powder 101 in FIG. 2) was filled inside the pressure molding die 300 . Inside the pressing die 300, a pressure of 300 MPa was applied to the solid electrolyte material according to Example 1 using the upper punch 301 and the lower punch 303. As shown in FIG.

While pressure was applied, the upper punch 301 and lower punch 303 were connected to a potentiostat (Princeton Applied Research, VersaSTAT4) equipped with a frequency response analyzer. The punch upper part 301 was connected to the working electrode and the terminal for potential measurement. The punch bottom 303 was connected to the counter and reference electrodes. The impedance of the solid electrolyte material was measured by electrochemical impedance measurement at room temperature.

FIG. 3 is a graph showing a Cole-Cole plot obtained by impedance measurement of the solid electrolyte material according to Example 1.

In FIG. 3, the real value of the impedance at the measurement point where the absolute value of the phase of the complex impedance was the smallest was regarded as the resistance to ion conduction of the solid electrolyte material. See the arrow R _se shown in FIG. 3 for the real value. The ionic conductivity was calculated based on the following formula (2) using the resistance value.
σ=( _Rse ×S/t) ⁻¹ (2)
Here, σ represents ionic conductivity. S represents the contact area of the solid electrolyte material with the punch upper part 301 (equal to the cross-sectional area of the hollow part of the frame mold 302 in FIG. 2). R _se represents the resistance value of the solid electrolyte material in impedance measurement. t represents the thickness of the solid electrolyte material (that is, the thickness of the layer formed from the solid electrolyte material powder 101 in FIG. 2).

The ionic conductivity of the solid electrolyte material according to Example 1, measured at 22° C., was 7.2×10 ⁻⁵ S/cm.

(X-ray diffraction)
4 is a graph showing an X-ray diffraction pattern of the solid electrolyte material according to Example 1. FIG. The results shown in Figure 4 were measured by the following method.

The solid electrolyte material according to Example 1 was sampled in an airtight jig for X-ray diffraction measurement in a dry argon atmosphere. Next, the X-ray diffraction pattern of the solid electrolyte material according to Example 1 was measured in a dry atmosphere having a dew point of −45° C. or less using an X-ray diffraction device (MiniFlex 600, manufactured by RIGAKU). Cu-Kα rays (wavelengths 1.5405 Å and 1.5444 Å) were used as the X-ray source.

In the X-ray diffraction pattern of the solid electrolyte material according to Example 1, peaks were present at diffraction angles 2θ near 26°, 30°, and 43°. This confirmed that the solid electrolyte material according to Example 1 had a crystal structure belonging to the space group Fm-3m. The crystal structure is presumed to be a sodium chloride type structure. Furthermore, the solid electrolyte material according to Example 1 has peaks at diffraction angles 2θ near 24°, 26°, 27°, 34° to 36°, 42°, and 46° to 47°. existed. This confirms that the solid electrolyte material according to Example 1 further has a LiAlCl ₄ -type structure belonging to the space group P2 ₁ /c. In FIG. 4, the peaks near 26° due to the crystal structure belonging to the space group Fm-3m and the crystal structure belonging to the space group P2 ₁ /c overlap. Although the solid electrolyte material according to Example 1 had the above peak, when X is F, Cl, or Br, even if it has a crystal structure belonging to the same space group Fm-3m, It is considered that the peak positions are back and forth.

(Production of battery)
In a dry argon atmosphere, the solid electrolyte material according to Example 1, Li ₄ Ti ₅ O ₁₂ , and carbon fiber (VGCF (manufactured by Showa Denko KK)) were prepared in a weight ratio of 65:30:5. rice field. These materials were mixed in a mortar. A mixture was thus obtained. VGCF is a registered trademark of Showa Denko K.K.

In an insulating cylinder having an inner diameter of 9.5 mm, Li ₆ PS ₅ Cl (80 mg), an algyrodite-type sulfide solid electrolyte, the solid electrolyte material according to Example 1 (20 mg), the above mixture (18 mg), and VGCF (2 mg) were layered in that order. A pressure of 740 MPa was applied to this laminate to form a solid electrolyte layer and a positive electrode.

Next, a metal In foil, a metal Li foil, and a metal In foil were laminated in this order on the solid electrolyte layer. A pressure of 40 MPa was applied to this laminate to form a negative electrode.

Next, current collectors made of stainless steel were attached to the positive and negative electrodes, and current collecting leads were attached to the current collectors.

Finally, an insulating ferrule was used to isolate the inside of the insulating cylinder from the outside atmosphere, and the inside of the cylinder was sealed. Thus, a battery according to Example 1 was obtained.

(Charging and discharging test)
5 is a graph showing the initial discharge characteristics of the battery according to Example 1. FIG. Initial charge/discharge characteristics were measured by the following method.

The battery according to Example 1 was placed in a constant temperature bath at 85°C.

A cell according to Example 1 was charged at a current density of 67 μA/cm ² until a voltage of 0.85 V was reached. This current density corresponds to a 0.05C rate.

The cell according to Example 1 was then discharged at a current density of 67 μA/cm ² until a voltage of 1.05 V was reached.

As a result of the charge/discharge test, the battery according to Example 1 had an initial discharge capacity of 846 μAh.

(Examples 2 and 3)
(Preparation of solid electrolyte material)
In Example 2, LiI, MgI ₂ , and AlI ₃ were prepared as raw material powders in a molar ratio of LiI:MgI ₂ :AlI ₃ =1.5:0.5:0.5.

In Example 3, LiI and MgI ₂ were prepared as raw material powders in a molar ratio of LiI:MgI ₂ =2:1.

Solid electrolyte materials according to Examples 2 and 3 were obtained in the same manner as in Example 1 except for the above matters.

(Composition analysis of solid electrolyte material)
The compositions of the solid electrolyte materials according to Examples 2 and 3 were analyzed in the same manner as in Example 1. The compositions of the solid electrolyte materials according to Examples 2 and 3 and the values corresponding to a in the compositional formula (1) are shown in Table 1.

(Evaluation of ionic conductivity)
The ionic conductivities of the solid electrolyte materials according to Examples 2 and 3 were measured as in Example 1. The measurement results are shown in Table 1.

(X-ray diffraction)
In the same manner as in Example 1, the X-ray diffraction patterns of the solid electrolyte materials according to Examples 2 and 3 were measured. The measurement results are shown in FIG.

(Charging and discharging test)
Batteries according to Examples 2 and 3 were obtained in the same manner as in Example 1 using the solid electrolyte materials according to Examples 2 and 3. The batteries according to Examples 2 and 3, like the battery according to Example 1, charged and discharged well.

(Comparative Examples 1 and 2)
(Preparation of solid electrolyte material)
LiAlI ₄ and LiI were prepared as solid electrolyte materials according to Comparative Examples 1 and 2, respectively.

(Evaluation of ionic conductivity)
The ionic conductivities of the solid electrolyte materials according to Comparative Examples 1 and 2 were measured in the same manner as in Example 1. The measurement results are shown in Table 1.

(X-ray diffraction)
In the same manner as in Example 1, the X-ray diffraction patterns of the solid electrolyte materials of Comparative Examples 1 and 2 were measured. The measurement results are shown in FIG.

(Discussion)
As is clear from Table 1, the solid electrolyte materials according to Examples 1 to 3 have a high ionic conductivity of 3.8×10 ⁻⁵ S/cm or more near room temperature.

A material containing Li, Mg, and I and containing a crystal phase having a crystal structure belonging to the space group Fm-3m has high ionic conductivity.

In the compositional formula (1), if 0≤a≤0.75 is satisfied, the solid electrolyte material has high ionic conductivity. As is clear from Examples 1 and 2, if 0.50≦a≦0.75 in the composition formula (1) is satisfied, the solid electrolyte material has higher ionic conductivity.

Since both Ga and In are elements of the same family as Al, even if the solid electrolyte material according to the first embodiment contains Ga or In as M, it can be expected that similar effects can be obtained.

Since F, Cl, and Br are all homologous elements to I, even if the solid electrolyte material according to the first embodiment contains F, Cl, or Br as X, similar effects can be obtained. I can expect it.

In all Examples 1 to 3, the batteries were charged and discharged at room temperature.

As described above, the solid electrolyte material according to the present disclosure is a material that can improve lithium ion conductivity, and is suitable for providing batteries that can be charged and discharged satisfactorily.

The solid electrolyte material of the present disclosure is used, for example, in batteries (eg, all-solid lithium ion secondary batteries).

REFERENCE SIGNS LIST 100 Solid electrolyte particles 101 Solid electrolyte material powder 201 Positive electrode 202 Electrolyte layer 203 Negative electrode 204 Positive electrode active material particles 205 Negative electrode active material particles 300 Pressure molding die 301 Punch upper part 302 Frame mold 303 Punch lower part 1000 Battery

Claims (9)

1. containing a crystalline phase containing Li, Mg, and X;
   here,
   X is at least one selected from the group consisting of F, Cl, Br, and I;
   The crystal phase has a crystal structure belonging to the space group Fm-3m,
   Solid electrolyte material.
2. The crystalline phase has a sodium chloride type structure,
   The solid electrolyte material according to claim 1.
3. The crystalline phase further contains M,
   Here, M is at least one selected from the group consisting of Al, Ga, and In.
   The solid electrolyte material according to claim 1 or 2.
4. M comprises Al;
   The solid electrolyte material according to claim 3.
5. X includes I,
   The solid electrolyte material according to any one of claims 1 to 4.
6. Represented by the following compositional formula (1),
   Li2 _{-aMg1- aMaX4 ( 1} )
   where 0≤a<1 is satisfied,
   The solid electrolyte material according to any one of claims 1 to 5.
7. In the composition formula (1), 0 ≤ a ≤ 0.75 is satisfied,
   The solid electrolyte material according to claim 6.
8. In the composition formula (1), 0.50 ≤ a ≤ 0.75 is satisfied,
   The solid electrolyte material according to claim 7.
9. positive electrode,
   a negative electrode, and an electrolyte layer disposed between said positive electrode and said negative electrode;
   with
   At least one selected from the group consisting of the positive electrode, the negative electrode, and the electrolyte layer contains the solid electrolyte material according to any one of claims 1 to 8,
   battery.

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